1. Field of the Invention
This invention relates to an image forming apparatus and, more particularly, to an apparatus for forming an image by processing image data in units of a plurality of samples.
2. Description of the Related Art
Apparatuses employing electrophotography have become increasingly popular as apparatuses for forming images. Electrophotography involves forming an image by scanning a photosensitive element with laser light or light from an LED that conforms to the value of image data. In an apparatus of this kind, the transmission of image data to a laser driver which drives a laser generally is performed in units of single pixels. However, advancements in image processing techniques have been accompanied by higher image processing speed and higher resolution, and it is desired that the speed at which image data is transferred to the laser driver be raised also in an image forming apparatus of the type which relies upon electrophotography.
In order to accommodate this demand for higher transfer speed, data consisting of a plurality of pixels (samples) is packed and then sent to the laser driver, thus making possible a substantial increase in transfer speed. However, when data of a plurality of pixels is transferred to the laser driver in the form of a pack in this manner, fine adjustment of scanning position in the main scan direction of the photosensitive element can only be performed in data pack units.
More specifically, in an image forming apparatus, particularly a color image forming apparatus having four photosensitive drums, in which colors are formed on the plurality of photosensitive drums in respective ones of the colors used and the color images are transferred to a single sheet of recording paper so as to overlap one another and form the final full-color image, the fact that adjustment cannot be made in units of single pixels means that it is not possible to adjust for a subtle positional deviation between colors in the formed image, where the offset is produced physically due to positional deviation in the positions at which the photosensitive drums or lasers for the various colors are disposed. As a consequence, a problem which arises is the formation of a poor quality image in which the positions of the color images that constitute the final full-color image do not coincide.